Superconductor technology: apparatus – material – process – High temperature devices – systems – apparatus – com- ponents,... – High frequency waveguides – resonators – electrical networks,...
Reexamination Certificate
1998-11-03
2002-11-19
Lee, Benny T. (Department: 2817)
Superconductor technology: apparatus, material, process
High temperature devices, systems, apparatus, com- ponents,...
High frequency waveguides, resonators, electrical networks,...
C333S0990MP, C333S202000, C333S219100, C505S700000, C505S866000
Reexamination Certificate
active
06484043
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dual-mode two-pole filter such as, for example a band pass filter for the microwave range, consisting of a resonator for two dipole modes each having a dielectric arranged on at least one high-temperature superconductive film, with a shielding housing arranged over the high-temperature superconductive film and enclosing the dielectric, and with a coupling device for coupling the dipole modes and in particular for coupling microwaves to the electromagnetic fields of the dipole modes employed. The invention, furthermore, relates to a multipole dual-mode filter.
2. Prior Art
In the satellite communications technology, band pass filters in the microwave range (4 to 20 GHz) play an important role in the preselection of individual communication channels. Analog multiplexers are usually employed there with filters based on hollow resonators, in connection with which the quality factors of the individual resonators are in the range of a few 10
4
. The hollow resonators, which have a circular cylindrical shape in most cases, are mostly operated in so-called “dual modes”, i.e., orthogonal dipole modes with preferred direction of the electromagnetic fields in the circular area. This loads to the fact that two poles of a filter can be realized with one resonator, i.e., an n-pole filter based on dual-mode resonators consists of n/2 resonators.
Now, in satellite communications technology, miniaturization of the filters is important on the one hand, and reduction of the insertion attenuation is important mainly for the output multiplexers on the other. This reduction in insertion attenuation leads to the fact that it is possible to reduce the high-frequency output of the output stages, which is normally generated by tube amplifiers (travelling-wave tube amplifiers). The insertion attenuation decreases with the increasing quality factor of the individual resonators.
A highly miniaturized dual-mode filter based on dielectric resonators is known from U.S. Pat. No. 4,489,293, where use is made of the HE
111
-mode of a cylindrical dielectric, which splits into two orthogonal dipole modes.
Further miniaturization of the arrangement described in the above state of the art is achieved, for example in that the cylindrical dielectric resonator is divided in half parallel with its base area and placed on a film consisting of high-temperature superconductors. The volume of the resonator is divided in half thereby (image plane).
The drawback of these arrangements lies in the fact that in the HE
111
-mode employed, the loss contributions of the metallic shielding housing lead to quality factors which are only in the range of 10
4
. The cause for this is the following:
The unstressed quality factor Q
0
of a dielectric resonator with metallic shielding is given by the expression
1/Q
0
=tan &dgr;+&Sgr;
R
s.i
/G
i
,
where tan &dgr; is the loss tangent of the material of the dielectric resonator. Some dielectrics such as sapphires, LaAlO
3
and rutile have tan&dgr;-values of a few 10
−6
or even less below a temperature of T=100 K, so that qualities between 10
5
and 10
6
would basically be possible with cooled dielectric resonators. However, the limitation is caused by losses in the various parts of the wall of the metallic shielding housing, such losses each being characterized by the surface resistance of the wall material R
S.i
as well as by a geometric factor G
i
for the particular part “i” of the wall. The geometric factor G; results from the distribution of the electromagnetic fields for the given mode of oscillation of the resonator. With the mode of oscillation employed in the aforementioned state of the art, the geometric factors are so low that the qualities for a copper housing with normal conductivity come to about 10
4
. The superconductive “image plane” did not lead to higher qualities because the losses dominated in the remaining parts of the wall with normal conductivity, and also in the dielectric.
Circularly cylindrical dielectric resonators with two end plates made of high-temperature superconductive films are known from WO 93/09575. Qualities in the range of 10
6
were demonstrated with such resonators because the geometric factor is adequately high for the normally conductive jacket surface of the cylinder in the TE
011
-mode used there. However, due to the rotation symmetry of the filed distribution, the mode is not a dipole mode, so that no “dual-mode” operation is possible in this case.
Therefore, the problem of the invention is to create a dual-mode filter in connection with which the quality factors for the individual resonators are about 10
5
to 10
6
.
SUMMARY OF THE INVENTION
According to the invention, the problem is solved for a dipole filter in that the dielectric has the shape of a hemisphere. The realization of more than two-pole filters is solved according to an arrangement where the spacing of at least two hemispherically shaped dielectrics defines the coupling between two resonators.
By shaping the dielectric according to the invention, the curved surfaces of the shielding housing have geometric factors which are sufficiently high for obtaining with one or two high-temperature superconductive films (HTS-films) the qualities required in connection with the problem on hand.
Additional embodiments of the present invention contain advantageous features for coupling to the electromagnetic fields of the dipole modes for equalizing the resonance frequency of the dipole modes as well as for adjusting the coupling between the dipole modes.
Additional advantages of the present invention are discussed below.
REFERENCES:
patent: 5179074 (1993-01-01), Fiedziuszko et al.
patent: 5324713 (1994-06-01), Shen
patent: 37 06 965 (1987-09-01), None
patent: 0 387 705 (1990-03-01), None
patent: 0 496 512 (1992-01-01), None
patent: 0 656 670 (1994-12-01), None
Pao, Chie-Shen et al.; “A Superconducting-Dielectric Resonator at W-Band”1988 IEEE MTT-S Syposium Digest;vol. 1; pp 457-458; May 1988.*
Patent Abstract of Japan, Patent No. 4-144302(A) “Band Pass Filter”, E-1259, Sep. 4, 1992, vol. 16, No. 420.
Patent Abstract of Japan, Patent No. 1-144701(A) “Dielectric Resonator”, E-817, Sep. 7, 1989, vol. 13, No. 404.
Nobuaki Imai et al “A Design Of High-Q Dielectric Resonators for MIC Applications” Electronics and Communications in Japan, vol. 67-B, No. 12, 1984 pp. 59-67.
N. Tellmann et al. “High-Q LaA1O3Dielectric Resonator Shielded by YBCO-Films” IEEE Transactions on Applied Superconductivity, No. 3, vol. 4, Sep. 1994, pp. 143-148.
Klein Norbert
Scholen Andreas
Collard & Roe P.C.
Forschungszentrum Jülich GmbH
Lee Benny T.
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